UV radiation suppresses the induction and elicitation of delayed-type hypersensitivity (DTH) in some individuals, but not all. We have developed a quantitative method using laser Doppler perfusion imaging analysis of UV-AB induced suppression of DTH using the elicitation response in previously tuberculin-PPD sensitized individuals in order to investigate the dose response relationship between UV dose and induction of suppression or resistance to UV induced suppression. Nineteen healthy volunteers were irradiated daily for four days on delineated areas on the upper back with UV-AB radiation. UV-AB dose levels were adjusted to deliver 60 or 120 mJ/ cm2 UV-B radiation. On the fourth day, one irradiated and one unirradiated test site for each UV-dose were chosen at random on each individual and injected intradermally with tuberculin. Test reactions were analyzed and quantified at j96 h clinically and with laser Doppler perfusion imaging. The results indicate that UV-AB radiation can suppress the elicitation phase of tuberculin delayed type hypersensitivity immune reaction and that there are dose dependent and individual differences in the immune suppressive effect of the UV- radiation. at low dose (UV-B), both the susceptible and resistant phenotypes were observed at an approximate ratio of 1:1. However, doubling the dose of UV-B increased the suppression in some individuals, induced suppression in others that were resistant, or induced a resistance or tolerance in others that were susceptible at the lower dose of UV. We hypothesize that the thresholds for UV induced suppression of DTH and the induction of T suppressor cells that may block elicitation vary considerably. Thus, characterization of both the UVR and the UVR dose response relationship for induction of susceptibility or resistance must be determined in order to adequately phenotype for these traits. These phenotypic differences in the human population may be used to determine if increased risks to skin cancer occurs in individuals who are suppressed.